1. Field of the Invention
The present invention relates to a system and method for producing nano-sized Fe powder, and in particular, to a system and method for producing nano-sized Fe powder having a polymer coated layer so as to prevent the powder from being oxidized under atmosphere.
2. Description of the Prior Art
Fine powder with magnetic properties has been applied to various fields, such as a contrast medium for a magnetic resonator, a recording medium for a magnetic tape, and a raw material for a magnetic fluid. Oxide based powders such as Fe2O3, Fe3O4, Fe-ferrite, Co-ferrite, etc have been commercially used as powders with magnetic properties.
Meanwhile, a pure iron powder has magnetization that is two or three times higher than the oxide-based powder, and has a relatively low anisotropy. Accordingly, a coercive force of the pure iron-based powder is lower than that of the oxide-based powder. Additionally, when a particle size of the pure iron powder is reduced to a single magnetic domain size, the magnetization of the pure iron-based powder is refined to a predetermined value, and the coercive force of the pure iron-based powder is simultaneously increased. Thus, it is possible to use the pure iron-based powder as a magnetic recording medium. Furthermore, when the particle size of the pure iron powder is further refined to a smaller size to act as a super-paramagnet, it can be used as a magnetic fluid.
Conventionally, a fine powder with magnetic properties has been most commonly produced according to a liquid phase reaction process, such as a metal hydroxide reduction process or a metal salt reduction process. Particularly, in the case of the high quality contrast medium and the magnetic fluid for a sealant, the particle sizes are the same as the single magnetic domain sizes or less, and thus, it can be produced using only raw powder having a super-paramagnetic property. Therefore, recently, there is an increased demand to develop a technology for producing fine powder which has lower particle size and improved magnetic properties.
To meet the above demand, Korean Pat. Application No. 2003-77589 has been filed by the applicant of the present invention, which discloses a method of producing a pure iron powder with a particle size of tens nm according to a gas condensing process. According to the above patent, an Fe-containing liquid precursor is gasified, Fe gas is separated from the gasified precursor, and the separated Fe gas is condensed to produce nano-sized Fe powder. However, an explosion may occur under atmospheric air in the course of collecting the Fe powder, after the Fe powder is produced according to the gas condensing process. Hence, in order to avoid such an explosion, it is necessary to enable the Fe powder to be subjected to a passivation treatment which forcibly feeds a small amount of oxygen into a chamber. An oxide layer is coated on a surface of the Fe powder, thereby resulting in safe treatment of the Fe powder under atmospheric air. However, the magnetic properties of an iron oxide layer coated on the surface of the Fe powder are very different from those of a pure iron core. Accordingly, it is difficult to gain the desired and intrinsic magnetic properties of the pure iron. Another disadvantage of the above patent is that when the Fe powder is used as the contrast medium, the iron oxide layer coated on the Fe powder is toxic to humans.